The polysilicon critical dimension (CD) is an important parameter in semiconductor fabrication. In particular, the critical dimension of the polysilicon determines the L.sub.eff which impacts the transistor properties. This parameter should be accurately controlled in a MOS fabrication facility.
The polysilicon linewidth may be typically determined by using the measured line resistance and sheet resistance of the substrate. Sheet resistance is measured in Ohms/square and is defined as the resistivity of the substrate divided by the substrate's thickness. The sheet resistance of a substrate is the resistance measured between the opposite sides of a square of that substrate.
The width of a polysilicon structure is typically calculated from the measured resistance of the polysilicon structure and the sheet resistance of the polysilicon structure. In particular, the width of the polysilicon structure may be determined from the following equation: EQU W.sub.poly =(R.sub..quadrature.poly L)/R.sub.poly
where R.sub.poly is the measured resistance of the polysilicon structure, L is the length of the polysilicon structure, R.sub..quadrature.poly is the sheet resistance of the polysilicon structure, and W.sub.poly is the width of the polysilicon structure.
The above-described techniques are not applicable to semiconductor fabrication processes utilized to produce semiconductor devices having a polysilicon and silicide structure less than 0.5 microns in width. More particularly, the sheet resistance of a refractory metal silicide structure becomes linewidth dependent for lines smaller than 0.5 microns in width.
Referring to FIG. 1, the sheet resistance of a refractory metal silicide structure is shown with respect to the linewidth of the refractory metal silicide structure. In particular, line 6 represents the sheet resistance of the refractory metal silicide structure in Ohms/square for a given range of linewidths from 0.25 microns to 0.8 microns. FIG. 1 shows that the sheet resistance of a refractory metal silicide structure becomes linewidth dependent for lines smaller than 0.5 microns in width.
To overcome this problem, conventional techniques used physical SEM measurements. Such techniques have significant drawbacks including being non-electrical, consuming substantial amounts of time and not allowing measurements after the semiconductor wafer is completely processed.
It would be desirable to overcome these and other drawbacks associated with the conventional methods of measuring the critical dimension of a refractory metal silicide structure.